Smoking Article

ABSTRACT

A smoking article ( 10 ) has a filter ( 20 ) located at one end, the filter comprising at least first, second and third sections ( 34,41,51 ) disposed in succession along a cylindrical axis of the smoking article. Each of the first ( 31 ) and third ( 51 ) sections includes at least one tube ( 35,55 ) running the length of the respective section, substantially parallel to the cylindrical axis of the smoking article. The second section ( 41 ) comprises material of substantially higher filtration efficiency than the tubes ( 35,55 ) of the first and third section. Ventilation ( 43 ) may be provided around the circumference of the filter in one or more zones.

FIELD OF THE INVENTION

The present invention relates to smoking articles such as cigarettes, and in particular to smoking articles that include a filter.

BACKGROUND OF THE INVENTION

When tobacco in a cigarette is burnt as the cigarette is smoked, tar is produced. In recent years, there has been a shift in consumer preference towards lower tar cigarettes. Accordingly, it is desirable to produce a cigarette that delivers less tar to the consumer.

Existing cigarettes have for many years included a filter that can help to reduce tar output. As the cigarette is smoked, the point of combustion moves closer to the filter. When the cigarette is first lit, the rod of unburnt tobacco itself provides a certain amount of filtration action, and can therefore help to reduce tar delivery. However, this action is lost as the tobacco rod is burnt to increasingly shorter lengths, resulting in increased smoke delivery for equivalent puff volumes during the latter puffs. It is also desirable to produce a cigarette that delivers less tar in the latter puffs to the consumer.

It is known to provide a hollow tube along a central axis of a portion of a filter. For example, GB 2177890 discloses a cigarette in which a filter comprises first and second elements, where the first element is adjacent the tobacco rod, and the second element is adjacent the mouth. The first element incorporates a thin central tube of heat-shrink material surrounded by cellulose acetate. When the cigarette is initially smoked, the tube provides a low resistance path to smoke through the first element (in preference to the smoke having to pass through the surrounding cellulose acetate). This low resistance path through the first element helps to compensate for the higher initial resistance of the long tobacco rod. However, as the cigarette warms up, the central tube collapses, and the vacated space is then occupied by expansion of the surrounding cellulose acetate material. The tube now no longer provides a low resistance path for smoke through the first element, with the smoke having to pass instead through the comparatively high resistance of the cellulose acetate of the first element.

A somewhat similar configuration is disclosed in EP 481596. In this document however, the tube does not collapse with heat. Rather, the tube is gradually blocked by smoke components that condense onto filter material at the end of the tube, whereupon the smoke must flow through the more resistant material around the filter. The tube may be provided with holes along its length to produce a more gradual transition.

The filtration properties of filters in existing cigarettes are largely independent of the amount of smoke presented to the filter, although there is a well-known relationship between flow and filtration efficiency. As a result, the performance of such filters, for example with respect to tar delivery, tends to vary with differing puff volumes and differing puff profiles.

SUMMARY OF THE INVENTION

The present invention provides a smoking article such as a cigarette having a filter located at one end. The filter comprises at least first, second and third sections disposed in succession along a cylindrical axis of the smoking article. Each of the first and third sections includes at least one tube running the length of the respective section. The second section comprises filter material of substantially higher filtration efficiency than the tubes of the first and third sections.

Such a filter can help to provide a more consistent level of tar, with a reduced dependency on the smoking regime or how much of the smoking article has already been consumed. For example, in one embodiment, the exit of the tube in the first section is at least partly blocked after a first amount of smoking Consequently more smoke now goes through the remainder of the first filter section (other than the tube), comprising some form of filter material. After a further amount of smoking, the entrance into the tube in the third section is at least partly blocked. More smoke is now routed through the remainder of the third filter section (other than the tube), again comprising some form of filter material. Accordingly, this embodiment provides a graduated and controlled rise in the filtration efficiency of the filter as the smoking article is consumed. Note that the rise in filtration efficiency occurs more rapidly for higher puff volumes and/or puff rates (since in this case the tubes block more quickly). In addition, the rise in filtration efficiency of the filter helps to compensate for reduced filtration by the unburnt tobacco rod itself as the smoking article is consumed.

In one embodiment, the tube(s) of the first section are coaxial with the tube(s) of the third section. The tubes of the first and/or third section may be located centrally within the smoking article (i.e. coaxial with the smoking article), or may be provided as grove(s) in the outer circumference of the filter. Another possibility is that a tube is located intermediate the centre and outside of the filter. The number and positioning of the tubes can be varied as desired to control the overall filter properties, and can vary from one filter section to another.

In one embodiment, the tube(s) of the first section and/or the third section have a diameter in the range 0.1-3 mm, or more particularly in the range 0.5-1.5 mm, and a length in the range 4-15 mm. The tube dimensions help to determine the overall properties of the filter. For example, it takes longer for a tube, and in particular the ends of the tube, with a greater diameter to become (at least partly) blocked during smoking. Accordingly, the tube dimensions can be adjusted depending on the desired properties of the filter and smoking article. Note that different tubes may have different dimensions (both in respect of tubes in different filter sections, and also in respect of multiple tubes in a single filter section).

In one embodiment, the tubes are hollow, and the first, second and third filter sections all comprise filter material, such as cellulose acetate, paper, and so on (different filter sections may comprise different filter material). For the first and third filter sections the filter material surrounds or embeds the tube(s) of these sections. The relative filtration efficiency of the filter material in the different sections can be used to control the overall properties of the filter. For example, in one embodiment, the filter material of the first filter section has a lower filtration efficiency than the filter material of the second and third filter sections. Consequently, the rise in filtration efficiency when a tube through the first filter section is at least partly blocked is smaller than the rise in filtration efficiency when a tube through the third filter section is at least partly blocked.

Ventilation may be provided around the circumference of the filter in one or more zones. The ventilation zone is preferably located downstream of a potential blockage point. In one embodiment, ventilation holes are provided on the outside of the second and/or third filter section. If the tubes through the first and third sections are centrally located (i.e. coaxial with the smoking article), then initially most of the airflow is along the central axis of the smoking article. However, as the ends of the tubes become at least partly blocked, and the flow of smoke is forced towards the outer portions of the smoking article, this increases the amount of air drawn in through the ventilation holes to dilute the smoke. In addition, the pressure differential, or pressure drop (PD), of the smoking article will increase. The positioning of the ventilation immediately downstream of the blockage points result in increased ventilation levels as the PD of the filter increases.

In one embodiment, the filter comprises additional pairs of sections in succession along the cylindrical axis of the smoking article after the third section. Each additional pair of sections comprises a first and second additional section. The first additional section includes at least one tube running the length of the first additional section, substantially parallel to the cylindrical axis of the smoking article. The second additional section comprises filter material of substantially higher filtration efficiency than the tube of the first additional section. Increasing the number of filter sections in this manner allows further control over the filter behaviour. For example, if a fourth and fifth filter section are provided analogous to the second and third filter sections, then the tube in fifth filter section will at least partly block some time after the tube in the third filter section becomes at least partly blocked. Such a filter therefore has more gradations in the rise of filter efficiency as respective tubes become blocked.

The invention also provides a filter for use in any smoking article such as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will now be described in detail by way of example only with reference to the following drawings:

FIG. 1 illustrates a cigarette filter in accordance with one embodiment of the invention.

FIG. 2 illustrates the behaviour of the cigarette filter of FIG. 1 for initial puffs in accordance with one embodiment of the invention.

FIG. 3 illustrates the behaviour of the cigarette filter of FIG. 1 for second stage puffs in accordance with one embodiment of the invention.

FIG. 4 illustrates the behaviour of the cigarette filter of FIG. 1 for third stage puffs in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is the schematic illustration of a cigarette 10 in accordance with one embodiment of the invention. Cigarette 10 has a generally cylindrical shape, and comprises a tobacco rod 15 (only shown partly in FIG. 1) joined to a filter 20 with an outer wrap 21. The filter is located at the mouth end 100 of the cigarette. The cigarette 10 is lit at the end of the tobacco rod 15 opposite to the mouth end.

Filter 20 comprises three sections 31, 41, 51 arranged along the cylindrical axis of the cigarette, where each section is cylindrical in shape. Section 31 is adjacent the tobacco rod 15, section 51 is adjacent the mouth end 100, and section 41 is between section 31 and section 51. The configuration of cigarette 10 is therefore determined by a succession of three planes, all perpendicular to the cylindrical axis of the cigarette. The first plane defines the boundary between tobacco rod 15 and the first filter element 31, the second plane defines the boundary between the first filter element 31 and the second filter element 41, and the third plane defines the boundary between the second filter element 41 and the third filter element 51. In one embodiment, the separation between the different planes (and hence the length of each filter section) is in the region 5-10 mm. (In other embodiments, the separation may be in the region 4-15 mm).

The first filter section 31 includes a tube 35 and the third filter section 51 also includes a tube 55. Tubes 35 and 55 are both coaxial with the cylindrical axis of the cigarette and each tube 35, 55 extends the length of its respective section. The radius of tubes 35, 55 is significantly less than the radius of the cigarette. For example, the diameter for the tubes may only be approximately 0.1-3 mm. In one embodiment, each of tubes 35, 55 has a diameter of approximately 0.5-1 mm. Note that if the radius of a tube is 20% of the radius of the cigarette as a whole, the cross-sectional area of the tube is only 4% of the cross-sectional area of the cigarette.

The tubes 35, 55 may be made of paper, cardboard, plastic or any other suitable material and may have a porous or non-porous surface. In the embodiment shown, the tubes 35, 55 are hollow, but in other embodiments may have a filling that offers very little resistance to airflow. In the embodiments shown, tubes 35 and 55 are substantially the same as one another, but in other embodiments may vary as appropriate in term of dimensions, shape and/or other properties.

In the first section 31, the tube 35 is surrounded by filter material 32 such as cellulose acetate, paper, polypropylene, or any other suitable material. This material is formed with a relatively low density, and hence a relatively low filtration efficiency (but significantly higher than the hollow tube). The middle section 41, which does not contain a central tube, also comprises a filter material 42 such as cellulose acetate, paper, or polypropylene, etc. This material is formed with a relatively high density, and so has a high filtration efficiency (compared to that of material 32). In the third section 51, the tube 55 is also surrounded by filter material 52 such as cellulose acetate, paper, polypropylene, etc. Again, this material is formed with a relatively high density, and so has a high filtration efficiency (compared to that of material 32).

The outer wrap 21 is provided with two circumferential rings of ventilation holes. The first ring of ventilation holes 43 is provided around the second section of the filter 41, while the second ring of ventilation holes 53 is provided near the start (i.e. away from the mouth end 100) of the third section of the filter 51. These ventilation holes allow air to be drawn into the cigarette filter and hence dilute smoke passing through.

FIG. 2 illustrates the main smoke flow through the cigarette 10 of FIG. 1, when the cigarette is first smoked, in accordance with one embodiment of the invention. Smoke from the burning tobacco travels down the tobacco rod 15 to filter 20. The smoke now passes through the tube 35 of the first element 31 in preference to passage through filter material 32, since tube 35 offers a lower resistance to the smoke flow. The smoke then passes through the high filtration efficiency material of the second section 41 before exiting at the mouth end 100 of the filter via the third section 51. In the third filter section 51, the smoke passes through the tube 55 in preference to the surrounding filter material 52, due to the lower flow resistance of tube 55.

At this stage, it is the second section 41 of filter 20 that provides the majority of the filtration activity of filter 20. This filtration activity is supplemented by the passage of the smoke through the relatively long portion of unburnt tobacco rod 15 prior to reaching the filter 20. Relatively little ventilating air is drawn in through ventilation holes 43, 53, since the main smoke flow through the cigarette is close to the central axis of the cigarette 10—i.e. away from the outside surface where the ventilation holes are located, and there is a low filter pressure drop upstream of the ventilation holes.

In the configuration of FIG. 2, smoke travels at a relatively high velocity through tube 35, due to the low flow resistance, and then decelerates on entry into the second section 41 where the filter material 42 offers a much higher flow resistance. This deceleration results in a concentration of smoke at impaction point 36—i.e. where the dense filter material 42 of the second element 41 is adjacent to the exit from tube 35. The raised concentration at impaction point 36 leads to a deposition of tar on filter material 42, which acts to increasingly block the exit from tube 35.

This leads to the situation shown in FIG. 3, in which tube 35 is blocked by the deposition of material at impaction point 36. (As used herein, “blocked” implies a partial or complete obstruction). Consequently, more smoke passing through the first filter section 31 now travels outside the tube 35 through the main body of the filter material 32, which occupies the outer annulus of the first filter section 31. This provides increasing filtration for the smoke travelling through the first filter section 31 (compared to when the smoke passed through tube 35 instead of filter material 32).

After having passed through filter material 32 of the first filter element 31, the smoke is drawn through the second element 41, and converges on the entrance 56 to tube 55. The smoke flow then passes through tube 55 as previously described in order to exit the filter 20 at mouth end 100.

The smoke flow through the second filter element 41 now passes somewhat closer to the ventilation holes 43 on the outside of the filter 20 (compared with the configuration of FIG. 2). This is because with the central tube 35 blocked (either completely or partly), more smoke exits the first filter section 31 nearer to the outside of the cigarette. The restriction of the end of tube 35 creates an increase in pressure drop in the filter section upstream of the ventilation holes, thereby increasing the amount of ventilating air entering the filter. In addition, as more smoke passes through the radially outer portions of the filter, adjacent to the incoming ventilating air, more smoke is deflected radially inwards by the ventilating air towards the central portion of the filter and across the filter material, thereby providing an increase in filtration efficiency.

The convergence of smoke towards the region 56 of the second filter adjacent to the entrance to tube 55 leads to an increased density of smoke at this impaction point. This rise in smoke concentration again causes the deposition of smoke materials such as tar into the filter material. Accordingly, as the cigarette is smoked further, there is a build-up of tar at location 56, which gradually blocks the entrance of tube 55 so that the exit of smoke from filter 20 via tube 55 is restricted.

This leads to the situation shown in FIG. 4. In the third filter section 51, with smoke flow through the central tube 55 now restricted, more smoke passes through the filter material 52 surrounding the central tube—i.e. through the outer annulus of the third filter section 51. The smoke is therefore subject to the high filtration efficiency of filter material 52. This helps to compensate for the reduced filtering within tobacco rod 15 (which is now substantially shorter in length than when the cigarette was first lit).

In the configuration of FIG. 4, the flow through the second filter section 41 is largely parallel to the cylindrical axis of the cigarette and is generally located in the (radially) outer portions of the filter, nearer to the ventilation holes 43 and 53. This increased flow adjacent to filtration holes 43 and 53, combined with the overall increase in pressure drop of the filter due to the (partial) blockage of the entrance of the tube 55, draws in increased ventilating air, resulting in greater dilution of the smoke reaching the mouth end 100.

The harder a cigarette is puffed, the more tar is generated, the faster the smoke exits tube 35, and the higher the impact filtration in FIG. 2. In addition, for each progressive stage, as smoke is gradually drawn towards the outer part of filter 20 and hence closer to ventilation holes 43, 53, the ventilation through filter 20 increases. Cigarette 10 therefore demonstrates an increase in filtration efficiency, pressure drop, and also ventilation with increased tar generation. Furthermore, cigarette 10 has a relatively flat puff by puff tar profile (based on the combined filtering of the filter 20 and remaining tobacco rod 15).

Although FIG. 1 illustrates one embodiment of the invention, the skilled person will be aware of many potential modifications of cigarette 10. For example, filter sections 31 and/or 51 may be provided with multiple tubes. In addition, the tube or tubes may not necessarily be located along the central axis of cigarette 10. For example, one possibility would be to have one or more grooves along the outer rim of the filter material 32 and/or 52 either to replace, or in addition to tubes 35/55 respectively.

Furthermore, although filter 20 comprises three sections, in other embodiments there may be additional sections. For example, a filter might be provided with a fourth section analogous to the second section, and a fifth section analogous to the third section. This would then provide a further gradation in the rise of filter efficiency.

It will be appreciated that the number, size, shape, material and structure of the tubes or grooves, the type and density of the filter material, and the number and structure of the filter sections can be adjusted to provide the desired overall filter characteristics—e.g. depending upon properties of particular tobacco, etc. In addition, although the present approach has been described generally in the context of cigarettes, it can be applied to a wider range of smoking articles, e.g. cigars. Accordingly, the scope of the present invention is defined by the appended claims and their equivalents. 

1. A smoking article having a filter located at one end, the filter comprising at least first, second and third sections disposed in succession along a cylindrical axis of the smoking article, wherein: each of the first and third sections includes at least one tube running the length of the respective section, and the second section comprises filter material of substantially higher filtration efficiency than the tubes of the first and third sections.
 2. The smoking article of claim 1, wherein the at least one tube of the first section is coaxial with the at least one tube of the third section.
 3. The smoking article of claim 1 or 2, wherein at least one tube of the first section and at least one tube of the third section are coaxial with the smoking article.
 4. The smoking article of any preceding claim, wherein at least one tube of the first section comprises a groove in the outer circumference of the filter.
 5. The smoking article of any preceding claim, wherein at least one tube of the third section comprises a groove in the outer circumference of the filter.
 6. The smoking article of any preceding claim, wherein the at least one tube of the first section has a length in the range 4-15 mm.
 7. The smoking article of any preceding claim, wherein the at least one tube of the first section has a diameter in the range 0.1-3 mm.
 8. The smoking article of claim 7, wherein the at least one tube of the first section has a diameter in the range 0.5-1.5 mm.
 9. The smoking article of any preceding claim, wherein the at least one tube of the third section has a length in the range 4-15 mm.
 10. The smoking article of any preceding claim, wherein the at least one tube of the third section has a diameter in the range 0.1-3 mm.
 11. The smoking article of claim 10, wherein the at least one tube of the third section has a diameter in the range 0.5-1.5 mm.
 12. The smoking article of any preceding claim, wherein the tubes are hollow.
 13. The smoking article of any preceding claim, wherein said first filter section other than said at least one tube comprises filter material.
 14. The smoking article of claim 13, wherein the filter material of the first filter section has a lower filtration efficiency than the filter material of the second filter section.
 15. The smoking article of any preceding claim, wherein said third filter section other than said at least one tube comprises filter material.
 16. The smoking article of claim 15, wherein the filter material of the third filter section has a higher filtration efficiency than filter material of the first filter section.
 17. The smoking article of any preceding claim, wherein ventilation holes are provided on the outside of the second filter section.
 18. The smoking article of any preceding claim, wherein ventilation holes are provided on the outside of the third filter section.
 19. The smoking article of any preceding claim, wherein the filter comprises additional pairs of filter sections in succession along a cylindrical axis of the smoking article after said third section, wherein each pair of sections comprises: a first additional section including at least one tube running the length of the first additional section, substantially parallel to the cylindrical axis of the smoking article; a second additional section comprising filter material of substantially higher filtration efficiency than the at least one tube of the first additional section.
 20. The smoking article of any preceding claim, whereby in use: the exit of the at least one tube in the first section is blocked after a first amount of smoking; and the entrance of the at least one tube in the third section is blocked after a further amount of smoking.
 21. The smoking article of any preceding claim wherein the tubes run substantially parallel to the cylindrical axis of the smoking article.
 22. A filter for use in the smoking article of any preceding claim.
 23. A filter for a smoking article, comprising a generally cylindrical filter body including first, second and third filter sections disposed in succession along the body each of the first and third sections includes at least one tube running the length of the respective section and the second section comprises filter material of substantially higher filtration efficiency than the tubes of the first and third sections. 